Sediments from the southern Caspian Sea, located in Iranian coast were examined on the basis of P-fractionation (five forms of phosphorus) by a sequential extraction scheme. Ninety-six surface sediment samples (for each season with triplicate) were collected from eight sampling transects in 10 and 100 m depths during summer and winter in 2010-2011. The result indicated that the most abundant forms of phosphorus were calcium bound phosphorus. Relative abundance of other forms of phosphorus follow the order: organic-P>Fe-P>Al-P>Absorbed-P. The loosely absorbed phosphorus represented <1% of the sedimentary inorganic phosphorus, while the Fe/Al phosphorus ranged 5–6%.The calcium bound phosphorus showed considerable contribution (88%) to the sedimentary inorganic P-loads
